Communications within buildings and other enclosed spaces have long presented problems. Communication wiring, such as for local area networks, is effective but suffers from problems with installation costs, limitations on connection locations and the need for periodic upgrading when technology advances. Metallic structural members, interior furniture, plumbing and electrical wiring all have a tendency to interfere with conventional wireless communications. Outside interference, such as galactic noise and human generated electromagnetic sources also frequently interferes with the quality and efficiency of in-building communications.
As described in the inventors prior application, a neglected frequency band in the electromagnetic spectrum, at least from the standpoint of communication utilization, is that in the 0.5-100 MHz range. Much of this range is traditionally considered to be less than useful, and is accordingly less regulated by government entities. An example of this in the United States is that Part 15 of the FCC Rules apply in this range. One reason that this range is not widely utilized is that the waveforms have sufficiently long wavelengths that structural interference affects transmission and reception. However, with the inventor's technology it has become possible to harness this range of frequencies and to turn the factors which have been hindrances into advantages.
An area of electromagnetic phenomena which has been little understood and utilized traditionally is that dealing with evanescent (non-propagating) waves. Commercial utilization of these phenomena have been rare. The phenomena are known and observed in waveguide technology, but are ordinarily a hindrance, and limit the utility of structure near what is known as “cut-off”.
Cut-off occurs for conventional propagation in hollow pipe waveguides when the size of the hollow pipe waveguide is less than one-half (½) of the wavelength at the operating frequency. When these conditions obtain, the transmission losses are very high but not infinite. The expression for attenuation below cut-off in ideal waveguides, Equation 1, may be written:γ=2π/λc√{square root over (1−(ƒ/ƒc)2)}  (1)where:
γ=attenuation
λc=cut-off wavelength
ƒ=operating frequency
ƒc=operating frequency at cut-off
where the wavelength, ƒ, is approximately equal to 11.8/ƒ(GHz) in inches.
As f is decreased below ƒc, γ increases from a value of 0 approaching the constant value of 2π/λc, when (ƒ/ƒc)2<<1.
The amount of attenuation is determined only by the cut-off wavelength of the waveguide, which is in general proportional to the transverse size of the waveguide, so that the value of γ may be made almost as large as one pleases by selecting a low cut-off wavelength (small pipe size). Since (1) holds for any wave in any shape of guide, it follows that choices of wave type and guide shape cannot influence the attenuation constant except in so far as they fix the cut-off wavelength λc {“Fields and Waves in Modem Radio”, Simon Ramo and John Whinney, pg 386-387, dated May 1956)
Wave motion, forming the core of many subjects in physics, is a prominent (interdisciplinary) topic in many textbooks. (ON EVANESCENT WAVES, A. Stahlhofen and H. Druxes, Univ. Koblenz, Inst. F. Physik, Rheinau 1, D-56075 Koblenz, Germany) While traditional wave motion is often dealt with in great detail (for good reasons), the theory of evanescent waves is often only mentioned in passing.
Such small mention is by no means justified: evanescent waves—originally indeed introduced as convenient mathematical tools having no application in mind (Bryndahl, O., “Evanescent waves im optical imaging”, in progres in Optics, American Elsevier Publishing Co, New York 1973, pp 169-221 and Hupert, J. J., Appl. Phys. 6 1975 pp 131-149)—matured in the last decades to a topic of its own intrinsic interest finding a steadily increasing number of applications in basic as well as applied research and in industry. Any propagating wave is converted into an evanescent wave when hitting a classically forbidden region (below cut-off). In this case, at least one component of the wave vector becomes imaginary or a complex value and the wave experiences exponential damping when operating in this region (the cut-off effect described above). Such waves are used as diagnostic tools in many contexts involving waveguides; applications range from diverse areas of solid state physics and microwave-technologies. Explicit examples show that evanescent waves play an important role in microwaves, optics, and quantum mechanics. Despite the fact that all of these systems are governed by different wave-equations, different dispersion laws, different energy regimes and completely different structures and sizes, wave motion in the respective systems under consideration often involves evanescent waves.
The typical mechanisms accounting for the existence of evanescent waves are: 1) conversion into other forms of energy in lossy media, 2) cut-off modes in certain directions resulting from reflections in lossless media, 3) gradual leakage of energy from certain guiding structures and 4) mode conversion produced by obstacles or by changes in guiding structures.
Evanescent waves have some peculiar properties sometimes defying intuition. As a typical example the fact was mentioned that they operate in the forbidden region (below cut-off) experiencing exponential damping. Wave motion involving evanescent waves is easily demonstrated with electromagnetic waves using microwaves.
It is now established that electromagnetic connectivity can be achieved by the use of evanescent non-propagating waves below cut-off or propagating waves above frequency cut-off. Some methodology must be developed which can inject currents into the metallic elements of a structure in order that evanescent waves be generated in the cut-off region. For frequencies above the cut-off region more traditional antenna technologies can be used.
Although the phenomena relating to evanescent waves and other wave characteristics resulting at wavelengths below or near cut-off regions are known, they have not heretofore been meaningfully commercially utilized. In general, these phenomena are considered to be hindrances and nuisances, rather than opportunities for actually enhancing communications. In this light, there remain many opportunities for utilization and improvement, to be addressed by the present invention and the Inventor's related inventions.